In what follows reference will be made for the sake of convenience to oysters, it being however understood that the invention is not limited to this example, but applies to any bivalve mollusk, such as clams, scallops, etc . . . . By this expression is meant any shellfish formed by an edible body enclosed in a shell having two valves which are closely applied one against the other. In the case of oysters, the valves are hinged together at one end, called the "heel", by means of a ligament hinge and are held closed by a powerful muscle which connects them together at a position slightly off-centered in direction from the opposite end to the heel and offset to the right, the oyster being seen from above.
Any operation for opening oysters, for consuming them, requires severing the retaining muscle. For this, oyster openers generally use a small knife with a sharp blade. This instrument is practically inefficient and even dangerous when it is used for the same purpose by an occasional operator such as the consumer.
The blade is forced into the joint between the valves in the vicinity of the muscle while a force is exerted on the knife in the direction of the oyster, so also in the direction of the hand which holds it. Accidents usually occur at that moment, when the blade slips on the shell following an error in detecting the joint, which can only be discerned with difficulty by an unpracticed eye because of the very undulating appearance of the laminations of the shell at the position considered.
Known oyster-openers intended for the general public, and some of which are widely available commercially, aim more or less at improving the protection afforded to the operator but not one gives real satisfaction.
They may be roughly classed in two categories depending on the method chosen for penetrating the shell by means of a cutting member for severing the muscle.
Instruments of the first category, derived from the previously mentioned knife, aim at dislocating and then separating the valves by means of a blade which is forced into the joint so as to reach the muscle.
Among these we find current commercial utensils, such as knives with a wide and pointed blade, having, at right angles to the working end of the handle, a guard for protecting against slipping of the blade on the shell. In fact, this guard only protects the hand which holds the blade and which in any case only risks being scratched by coming into contact with the shell, as opposed to the other hand which, holding the oyster, is directly exposed to the blade of the knife.
The use of a protecting glove for the hand holding the oyster has also been thought of. But the inevitable rigidity of the glove penalizes the ease of the opening operation in favor of safety of the operator which remains however limited.
Instruments of the second category proceed, not by separating the valves, but by removing a portion of the shell so as to form therein an opening through which a cutting element is then inserted so as to cut the muscle. Removal of material may be made either by cutting the end opposite the heel by means of cutting pincers (French patent application No. 1 536 939), or by removing a small disk from the upper flat valve in the immediate vicinity of the muscle by means of a tubular punch in which slides a wire cutting by rotation (French patent application Nos. 2 173 803 and 2 383 635).
In addition to the disadvantages related to the operating difficulties or to the appearance of oysters opened under such conditions, these devices do not seem capable of ensuring the indispensable cleanliness of the edible body because of shell waste or fragments which make it unclean and even dangerous to eat.
A device is further known common to the above-mentioned categories in that it works by dislocating and separating the valves in the vicinity of the muscle by means of a penetrating member, separate from the element for severing the muscle.
This device, described in French patent application No. 1 464 856, is formed of a handle equipped with a working head provided with a short blade disposed beside a conical motor driven borer. As the instrument is brought closer to the oyster, the borer gradually separates the valves during introduction thereof, while the blade, set slightly back, severs the muscle.
In fact, this instrument cumulates in a certain way the respective disadvantages of the two above-mentioned categories.
Indeed, the difficulties of initially positioning the point of the borer in the joint and the consequences thereof often unfortunate for the operator remain in their entirety.
Moreover, the rotating borer which penetrates inside the oyster may take with it fragments torn from the edges of the valves and, similarly, break up the edible body, thus making it unfit for consumption, or at least unfit to comply with the criteria of presentation of the oyster demanded by consumers.
Moreover, the motor of the borer, as well as the transmission members are placed inside the handle, so that this latter forms more a protective case than a gripping handle adapted to comply with the ergonomic requirements of a handle.
We can then see, through this brief analysis of the state of the art, that the "oyster-opening" utensils intended for the general public show a real incapacity for providing correctly and conjointly the contradictory requirements which are the ease of opening of the shell, the safety of the operator and the presentation of the oyster, not only from the aesthetic point of view but also from the point of view of cleanliness of the edible body.